Thank you Sarah, Maw, Davida and others..
I'm not usually a mother-of-the -bride outfit person to be honest and wouldn't be comfortable in some more "traditional" outfits. I don't like many synthetic fabrics and find synthetic gauzy ones the worst. Lots of lace is very poor quality unless you pay an arm and a leg...
I wore an Ann Balon 3 piece (skirt, camisole and jacket to one daughter's wedding and was able to wear those pieces separately for years. I wore a nice top, with crop trousers to another (with a great hat) - but this one is a very "fancy" do... and I'm stumped to be honest.
There will be a lot of very well outfitted guests there. I don't want to "let the side down" but can't justify buying one-use-only items.
Maybe I need a crash diet? Would that do some bust/belly shrinking I wonder? 
I do appreciate the suggestions.
Thank you all.